failure analysis of cerebral aneurysm mohd yusrizal...

FAILURE ANALYSIS OF CEREBRAL ANEURYSM

MOHD YUSRIZAL BIN MOHD YUSOOF

Thesis submitted in fulfillment of the requirements for the award of the degree of

Bachelor of Mechanical Engineering

Faculty of Mechanical EngineeringUNIVERSITI MALAYSIA PAHANG

DISEMBER 2010

ii

UNIVERSITI MALAYSIA PAHANG

FACULTY OF MECHANICAL ENGINEERING

I certify that the project entitled “Failure Analysis of Cerebral Aneurysm” is written

Mohd Yusrizal B. Mohd Yusoof. I have examined the final copy of this project and in

our opinion; it is fully adequate in terms of scope and quality for the award of the degree

of Bachelor of Engineering. I herewith recommend that it be accepted in partial

fulfillment of the requirements for the degree of Bachelor of Mechanical Engineering.

(Mohd Fadzil bin Abdul Rahim) ....................................

Examiner Signature

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SUPERVISOR’S DECLARATION

I hereby declare that I have checked this project and in my opinion, this project is

adequate in terms of scope and quality for the award of the degree of Bachelor of

Mechanical Engineering

Signature :

Name of Supervisor : Mohd Akramin Bin Mohd Romlay

Position : Lecturer

Date :

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STUDENT’S DECLARATION

I hereby declare that the work in this project is my own except for quotations and

summaries which have been duly acknowledged. The project has not been accepted for

any degree and is not concurrently submitted for award of other degree.

Signature :

Name : Mohd Yusrizal Bin Mohd Yusoof

ID Number : MA08148

Date :

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ACKNOWLEDGEMENTS

I would like to thank all people who have helped and inspired me during completed this studies.

I especially want to thank my supervisor; Mr. Mohd Akramin Bin Mohd Romlay, for his guidance during completed this project. His perpetual energy and enthusiasm in supervising had motivated his entire student, including me. In addition, he was always accessible and willing to help his students with their project. As a result, this project can be completed.

My deepest gratitude goes to my family for their unflagging love and support throughout our life; this dissertation is simply impossible without them and also to my love Siti Hana Bte Mohamad Yusoff.

All of my friends at the University Malaysia Pahang made it a convenient place to study. In particular, I would like to thank all friend for their knowledge and help in order to complete this studies.

Last but not least, thanks to God for giving us living in this universe and provide us with all necessary things.

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ABSTRACT

The aneurysm is the abnormal bulging of a portion of an artery due weakness in the cerebral at the circle of Willis brain. Nowadays, cerebral aneurysm is the one of the disease which have killed the people very quickly. This occurs when the mechanical behavior exceeds the strength of the tissue. This study is focused on cerebral aneurysm. Investigations on the changes of flow phenomena and the mechanical behavior in cerebral aneurysm have been studied. By using the simulation tools, the stress behavior on this region has been analyzed. The normal size of cerebral diameter is about 3-7 mm and aneurysm can bulge and reach until 10 mm. The velocity profile, nodal pressure distribution, displacement of wall and the stress at the wall had been identified at locations of aneurysm. As the size of an aneurysm increases, there was a potential of rupture of aneurysm. This can result in severe hemorrhage or even worst, fatal event.The studies are proceed based on numerical approach. The result shown that mechanical behaviors inside aneurysm region would be different compare to the normal blood vessel. It was proved that the maximum velocity had been obtained is 0.192 m/s. The maximum displacement of wall aneurysm at the neck is 0.00005 mm and the maximum affective stress at the aneurysm is 21.70 MPa. For the pressure distribution, the highestpressure at the aneurysm is 15.6 KPa. This study would help to predict cerebral aneurysm and provide better understanding about the cerebral aneurysm.

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ABSTRAK

Aneurisme merupakan satu salur darah dibahagian kepala yang mengalami keadaan bengkak. Gejala ini memberi kesan yang buruk kepada pesakit yang boleh menyebabkan salur darah tersebut menjadi lemah. Pada masa kini penyakit ini telah menyerang dan membunuh manusia dengan begitu cepat. Perkara ini terjadi apabila keadaan mekanikal telah melebihi keadaan asal pada salur darah tersebut. Ini kerana para doktor masih tidak dapat menyelesaikan masalah ini. Simulasi akan dijalankan dengan mengambil model salur darah ditengah otak. Kajian ini telah menfokuskan kepada keadaan mekanikal pada salur darah. Saiz normal salur darah di bahagian tengah otak adalah 3-7 mm dan pembengkakkan boleh berlaku sehingga 10 mm. Apabila saiz aneurisme meningkat, terdapat potensi untuk aneurisme pecah. Ini boleh menyebabkan pendarahan atau lebih teruk, iaitu kematian. Kajian ini hanya dijalankan dengan pendekatan pengiraan matematik tanpa melibatkan sebarang eksperimen. Berdasarkan kajian telah ditunjukkan bahawa sifat-sifat mekanikal di dalam bahagian aneurismeadalah berbeza dengan salur darah yang normal. Jelaslah terbukti bahawa halaju pada aneurisme adalah 0.192 m/s. Anjakan paling tinggi adalah 0.00005 mm dan tekanan paling tinggi adalah 21.70MPa. Tekanan berkesan paling tinggi adalah 15.6 KPa. Dengan mengkaji sifat-sifat mekanikal di bahagian salur darah aneurism yang sebenar dapat memberikan maklumat-maklumat yang berguna mereka untuk lebih memahami keadaan aneurisme yang sebenar.

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TABLE OF CONTENTS

PAGE

EXAMINER ii

SUPERVISOR’S DECLARATION iii

STUDENTS’S DECLARATION iv

ACKNOWLEDGEMENT v

ABSTRACT vii

ABSTRAK viii

TABLE OF CONTENTS xi

LIST OF TABLES xii

LIST OF FIGURES xiii

LIST OF ABBREVIATIONS xv

CHAPTER 1 INTRODUCTION

1.1 Cerebral Aneurysms 1

1.2 Aneurysm 3

1.2.1 Symptoms of Cerebral Aneurysm 51.2.2 Risks of Aneurysm 5

1.3 Problems Statement 6

1.4 Objectives 7

1.5 Scopes 7

CHAPTER 2 LITERATURE REVIEW

2.1 Cerebral Aneurysms 8

2.2 Finite Element Analysis (FEA) 10

2.2.1 Geometry 112.2.2 Material Model 122.2.3 Boundary Condition 15

2.3 Computation Fluid Dynamics (CFD) 16

2.3.1 Blood Flow 16

x

2.3.2 Mathematical and Numerical. 17

2.4 Fluid-Structure Interaction (FSI) 20

2.5 Summary 20

CHAPTER 3 METHODOLOGY

3.1 Introduction 20

3.2 Project Planning 20

3.3 Model Design 21

3.4 Model Analysis 22

3.4.1 Finite Element Analysis Of Cerebral Aneurysm 223.4.2 Formulation Of Cerebral Aneurysm. 243.4.3 Material Model 253.4.4 Simulations Assumption, Parameter And Boundary Conditions

253.4.5 Boundary Condition 26

3.5 Computation Fluid Dynamics (CFD) 27

3.5.1 Blood Flow 28

3.6 Fluid-Structure Interaction (FSI) 28

3.7 Software Application 29

3.8 Summary 29

CHAPTER 4 RESULTS AND DISCUSSION

4.1 Introduction 31

4.2 Mechanical Behavior in Cerebral Aneurysm 31

4.3 Displacement wall of Cerebral Aneurysm 32

4.4 Stress Distribution at the Cerebral Aneurysm 34

4.5 Pressure Distribution at Neck of Aneurysm 37

4.6 Interaction between Flow and Wall Deformation 38

4.7 Summary 40

CHAPTER 5 CONCLUSION

5.1 Conclusion 41

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5.2 Limitations 41

5.3 Recommendations 42

REFERENCES 43

APPENDIX A1 50

APPENDIX A2 53

APPENDIX B 71

xii

LIST OF TABLES

Table No. Title Page

3.1 Parameter of cerebral aneurysm 24

3.2 Parameter of cerebral aneurysm 26

4.1 Simulation result using Adina software with diameter 65mm 29

4.2 Result simulation 31

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LIST OF FIGURES

Figure No. Title Page

1.1 Circle of Willis 2

1.2 Circle of Willis 3

1.3 Type of aneurysm 5

2.1 The geometry of simplified aneurysm containing the two part 12

2.2 Artificial model 12

2.3 The cerebral arterial system in the bottom view of brain and

schematic representation of the main arteries

13

2.4 The anatomy of healthy artery wall 14

3.1 Flow chart shown the overall flow of the process of this

project

21

3.2 Geometry of dilated vessel 24

3.3 Graph velocity versus length 26

4.1 The flow phenomena in cerebral aneurysm 29

4.2 Displacement of cerebral aneurysm 30

4.3 Graph Displacement and velocity versus diameter of cerebral

aneurysm

31

4.4 Wall displacement distribution 32

4.5 Stress distribution at the cerebral aneurysm 33

4.6 Effective stress 33

4.7 Graph displacement and stress versus velocity of cerebral

aneurysm

34

4.8 Graph displacement and effective stress versus velocity of

cerebral aneurysm

34

4.9 Graph nodal pressure versus velocity of flow 35

4.10 Red circle shown that the nodal pressure at the neck of

aneurysm at blue circle.

36

4.11 Graph velocity of flow versus displacement of cerebral

aneurysm.

37

4.12 Velocity profile in cerebral aneurysm 37

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4.13 Enlargement of velocity profile in cerebral aneurysm 38

6.1 Manual user SolidWork2009 45

6.2 Diameter of circle 45

6.3 Extrude the circle 46

6.4 Dome at the middle cylinder 46

6.5 Save fail type 47

7.1 Invoke the AUI Adina 48

7.2 Analysis assumption of kinematics 49

7.3 Import parasolid file 50

7.4 Select the parasolid file 50

7.5 Structure of model 51

7.6 Apply fixity column 51

7.7 Defining the material for the solid model 52

7.8 Define element group 53

7.9 Meshing of the body 54

7.10 Create the Adina input file 54

7.11 Adina CFD 55

7.12 Number of iteration 56

7.13 Automatic Time-Stepping for Transient Analysis 57

7.14 Time step of the simulation 58

7.15 Time function of the simulation 58

7.16 Time function data for pressure specified conditions 59

7.17 Time function data for velocity specified conditions 59

7.18 Import parasolid file for fluid model 60

7.19 Applying the normal traction for the fluid model 61

7.20 Applying the velocity for the fluid model 62

7.21 Define material properties for the fluid model 63

7.22 Define element group 64

7.23 Final result of the analysis 65

xv

LIST OF ABBREVIATIONS

CA Cerebral Aneurysm

CFD Computational Fluid Dynamics

FEA Finite Element Analysis

FSI Fluid Structure Iteraction

CHAPTER 1

INTRODUCTION

1.1 CEREBRAL ANEURYSM

Cerebral aneurysms are localized dilatations of the intracranial arterial wall that

usually occur on or near the circle of Willis as shown in Figure 1.1. Rupture of intra-

cranial aneurysms is the leading cause of subarachnoid hemorrhage and often causes

significant mortality and morbidity. Solid biomechanical analysis of patient-specific

cerebral aneurysms and estimations of wall stress distribution can provide useful in-

sights into the disease process and help quantify geometric features within a physics-

based framework. Investigations on solid biomechanics of intracranial aneurysms (ICA)

have been scarce unlike for abdominal aortic aneurysms (Wang et al., 2009). The bio-

mechanics of aneurysm has been studied with great interest since aneurysm rupture is a

mechanical failure of the degenerated aortic wall and is a significant cause of death in

developed countries (David et al., 2006). Rupture of cerebrovascular lesions does not

occur very frequently, but when the disease has severe consequences for the individual.

Thus, there is an urgent need to understand the etiology of these lesions and to establish

reliable criteria by which surgeons can predict the risk of rupture and thus the need for

operation (Austin et al., 1993). Besides that, the infection can lead the body to wide ill-

ness. The greatest danger of an aneurysm is rupture, which is often a fatal event.

Cerebral aneurysms are frequently observed in the outer wall of curved vessels.

They are found in the internal carotid artery, near the apex of bifurcated vessels includ-

ing the anterior communicating artery (ACA), anterior cerebral artery and the middle

cerebral artery (MCA). Cerebral aneurysms disease has been reported to affect around

one to five percent of the population.

Although many cases of this disease are unruptured, the catastrophic consequences of

subarachnoid hemorrhage (SAH) following rupture of cerebral aneurysms make optimal

treatment of patients. Rupture of a cerebral aneurysm can be dangerous for a patient and

occurs most commonly between 40 and 60 years of age. When an aneurysm ruptures,

blood leaks from the ruptured wall into the subarachnoid space, or the brain itself, p

tentially causing serious damage. Aneurysm growth and rupt

factors; geometrical factors such as aneurysm size and shape or the ratio of the ane

rysm dome height to the neck width,

of structural proteins of the extracellular matrix in the intracranial arterial wall; and h

modynamic factors, especially wall shear stresses

Aneurysms come in a variety of shapes and siz

berry aneurysm as shown in

Figure 1.1: Circle of Willis

Source: Paal et al., 2007


hemorrhage (SAH) following rupture of cerebral aneurysms make optimal



the ruptured wall into the subarachnoid space, or the brain itself, p

tentially causing serious damage. Aneurysm growth and rupture depends on multiple

geometrical factors such as aneurysm size and shape or the ratio of the ane

the neck width, biological factors such as decreased concentration

of structural proteins of the extracellular matrix in the intracranial arterial wall; and h

modynamic factors, especially wall shear stresses

Aneurysms come in a variety of shapes and sizes. The most common ty

berry aneurysm as shown in Figure 1.2 and Figure 1.3. It is round like

2


hemorrhage (SAH) following rupture of cerebral aneurysms make optimal



the ruptured wall into the subarachnoid space, or the brain itself, po-

ure depends on multiple

geometrical factors such as aneurysm size and shape or the ratio of the aneu-

biological factors such as decreased concentration

of structural proteins of the extracellular matrix in the intracranial arterial wall; and he-

es. The most common type is a

. It is round likes a berry and con-

3

nected to the artery by a stem or neck. There are two general types of aneurysms, fusi-

form and saccular. A fusiform aneurysm is spindle-shaped without a neck. The saccular

aneurysms are the most frequent cerebral aneurysms showing a berry like outpouching

of the vessel wall: they often develop at the curved side of the vessels or at the apex of

bifurcations. A giant aneurysm is like a berry aneurysm, but it is large about one and

half inches or three centimeters or more in diameter.

Figure 1.2: Circle of Willis


1.2 ANEURYSMS

Aneurysms are blood-filled dilation (balloon-like bulge) of a blood vessel caused

by disease or weakening of the vessel wall. Aneurysms most occur in arteries at the

base of the brain (the circle of Willis) and in the aorta (the main artery coming out of

the heart, a so-called aortic aneurysm). A sign of an arterial aneurysm is a pulsating

4

swelling that produces a blowing murmur on auscultation (the act of listening for

sounds in the body) with a stethoscope.

There are four main locations where aneurysms always happen that are Cerebral

Aneurysms or Brain, Aorta Aneurysms, Abdominal Aneurysms and Thoracic Aortic

Aneurysms. As the size of an aneurysm increases, there is an increased risk of rupture,

which can result in severe hemorrhage or other complications including sudden death.

Severe bleeding can occur if the aneurysms break or rupture. Not all aneurysms are life-

threatening. But if the bulging stretches the artery too far, this vessel may burst, causing

a person to bleed to death. An aneurysm that bleeds into the brain can lead to stroke or

death. Aneurysms usually appear in either fusiform or saccular as shown in Figure 1.3.

A fusiform aneurysms is spindle shaped without a neck. While, the second type of

aneurysms is saccular. The saccular aneurysms are the most frequent cerebral aneu-

rysms showing a berry like outpouchings of the vessel wall: they often develop at the

curved side of the vessels or at the apex of bifurcations.

Saccular

Fusiform

Figure 1.3: Types of Aneurysms


5

1.2.1 Symptoms of Cerebral Aneurysm

Symptoms will depend upon the location of the aneurysm. Common sites that

aneurysms occurred include the abdominal aortic artery, the intracranial muscles (sup-

plying blood to the brain), and the aorta (supplying blood to the chest area). Many aneu-

rysms are present without symptoms and are discovered by feeling or on x-ray films

during a routine examination. When symptoms occur, they include a pulsing sensation,

and there may be pain if the aneurysm is pressing on internal organs. If the aneurysm is

in the chest area, for example, there may be pain in the upper back, difficulty in swal-

lowing, coughing or hoarseness. A ruptured aneurysm usually produces sudden and se-

vere pain, and depending on the location and amount of bleeding, shock, loss of con-

sciousness and death. Emergency surgery is necessary to stop the bleeding.

In some cases, the aneurysm may leak blood, causing pain without the rapid de-

terioration characteristic of a rupture. Also, clots often form in the aneurysm, creating

danger of embolisms in distant organs. In some cases, the aneurysm may dissect into the

wall of an artery, blocking some of the branches. Dissecting aneurysms usually occur in

the aortic arch (near its origin, as it leaves the heart) or start in the descending thoracic

portion of the aorta after it gives off the branches to the head and arms. Symptoms vary

according to the part of the body that is being deprived of blood; they are usually sud-

den, severe and require emergency treatment.

1.2.2 Risks of Aneurysm

It is not clear exactly what causes aneurysms. However some theories and risk fac-

tors had been defined. The condition that causes the walls of the arteries to weaken can

lead to an aneurysm.

i. Genetic factor.

ii. Smoking

iii. High blood pressure

iv. High cholesterol

v. Gender factor. Male gender is likely to have aneurysm than female.

6

vi. Obesity

Aneurysms develop slowly over many years and often have no symptoms. Some-

times people do not realize they have an aneurysm that can lead to rupture. The symp-

toms of rupture include:

i. Abdominal mass

ii. Abdominal rigidity

iii. Headache

iv. Anxiety

v. Clammy skin

vi. Nausea and vomiting

vii. Pain in the abdomen or back, severe, sudden, persistent, or constant.

viii. Ringing in the ears

ix. Pulsating sensation in the abdomen

x. Rapid heart rate when rising to a standing position

xi. Shock

1.3 PROBLEMS STATEMENT

Nowadays, the case of rupture of celebrals is increasing every years and it often oc-

curs without any preceding symptoms. The rupture occurs when the stress acting artery

on the brain exceeds the strength of the artery wall itself. It was necessary to establish

reliable criteria of the rupture risk assessment procedures in cerebral for these lesions,

and criteria based on the mechanical field. Besides that, the prediction of rupture hap-

pens is not available yet. The stress distribution caused by pressure in the artery is one

element factor that influenced the rupture of aneurysm. So it was necessary to study the

behavior of these elements to better understanding of aneurysms.

7

1.4 OBJECTIVE

The objectives of this research are;

To determine maximum displacement at the wall cerebral aneurysm.

To determine stress distribution in cerebral aneurysm.

To determine the maximum pressure in the cerebral aneurysms.

1.5 PROJECT SCOPE

This project is to investigate the condition of wall ruptured in cerebral with

ADINA software. A model of cerebral with shape was created with geometry in 3D.

The flow and structure of model of cerebral aneurysm are analyzed by using Fluid-

Structure Interaction of ADINA software. The flow in cerebral, only the aneurysm from

artery brain area were selected. For this case, the project is focused on steady state of

analysis of fluid structure iteration.

CHAPTER 2

LITERATURE REVIEW

2.1 CEREBRAL ANEURYSMS

Arterial aneurysms are localized dilatations of blood vessels caused by a

congenital or acquired weakness of the media. A variety of characteristic geometries

can be distinguished. In the cerebral arteries the most common type is the saccular

aneurysm, having a bubble-like geometry. Most cerebral aneurysms are asymptomatic

and therefore remain undetected (Johnston, 2002). Autopsies have revealed that many

as 25% of the population older than 55 years undetected saccular aneurysms are found

(Rubin and Farber,1999). In the general population approximately 5% is likely to harbor

these aneurysms and 15-20% of these persons have multiple lesions (Kyriacou, 1996;

Lieber et. al., 2002). Cerebral aneurysms are highly uncommon in people younger than

20 years and very common in older people, especially above 65 years old (Lieber et al.,

2002). This indicates that not every aneurysm is life threatening. However, rupture of an

intracranial aneurysm results in subarachnoid hemorrhage (SAH), with 35% mortality

during the initial hemorrhage (Rubin et al., 1999). In case of subsequent hemorrhage the

prognosis is even worse. A total 50 to 60% of the patients with SAH will die or suffer

severe morbidity (Lieber et al., 2002). Not more than one third of the patients

eventually return to their previous occupation due to severe neuropsychological

disabilities (Lieber et al., 2002).

According to (Koivisto et al., 2000) no significant difference was detected in the

outcome one year after surgical or endovascular treatment of ruptured cerebral

aneurysms. The first outcomes of the ongoing International Subarachnoid Aneurysm

Trial (ISAT), a large scale trial on ruptured aneurysms involving 42 centers in Europe

9

and America, reported that the relative risk of death or significant disability for

endovascular patients is 22.6% lower than for surgical patients. In unruptured

aneurysms coil embolization resulted in significantly less complications than surgical

clipping (Johnston, 2000).

The decision whether intervention is recommended depends on the balance

between the risk of rupture and the risk related to the intervention itself. The mechanical

properties and loading state of the arterial wall are most important in the determination

whether rupture of the aneurysm is a serious threat. Since both parameters not be

determined adequately in vivo, accurate estimation of the risk of rupture is not possible

yet. At present, the risk of rupture is mainly associated with the maximum dimension of

the lesion even though there is controversy over the 'critical size' (Kyriacou et al.,

1996).

The loading state of the arterial wall depends on the pressure load and shear

stress. In contrast to shear stress, the pressure load is similar throughout the arterial

system. The shear rate introduced by intra-aneurysm blood flow is known to affect the

endothelial cells covering the lumen. This induces adaptation, or in aneurysms,

degradation of the arterial wall. Since the shear rate can be determined from the intra-

aneurysm flow, the development of efficient methods for in vivo flow measurements is

of interest. X-ray systems have great potential in becoming an important non-invasive

method to determine the flow properties (Kyriacou et al., 1996). However, injection of

contrast agents is required in X-ray flow visualization techniques. Knowledge on the

influence of these injections is indispensable for proper interpretation of the X-ray

images, and can be acquired via computational studies. As the intra-aneurysm flow

patterns are complex, in vitro validation is needed to obtain insight in its accuracy and

limitations. Recent studies have introduced Fluid Structure Interface (FSI) simulations

using isotropic wall properties to map regions of stress concentrations developing in the

aneurismal wall as a much better alternative to the current clinical criterion Detailed

hemodynamic in cerebral aneurysms have been investigated experimentally and

computationally to understand better the mechanisms contributing to the aneurysm

progression (Kyriacau et al., 1996). However, the mechanisms causing aneurysm still

remain to be unveiled. One of the main findings regarding aneurysm hemodynamic so

10

far is the sensitivity of the blood flow to the vascular morphology. In addition using FSI

analysis from the previous study, dynamic change in vascular morphology and

hypertensive blood pressure, which is one of the risk factors in subarachnoid

hemorrhage, affects the hemodynamic. Thus, the importance of FSI in cerebral

aneurysms is still debated because the human intracranial arteries are stiffer than the

other arteries (Paal et al., 2007), and it was asserted in an earlier computational

angiographical study that the impact of vascular motion on the hemodynamic is not

crucial.

2.2 FINITE ELEMENT ANALYSIS (FEA)

Finite element analysis is a powerful computer-based tool widely used by

engineers and scientists for understanding the mechanics of physical systems. Finite

element analysis consists of a computer model of a material or design that is stressed

and analyzed for specific results. Mathematically, the finite element analysis is used for

finding approximate solutions of partial differential equations as well as of integral

equations. In order to present unlimited degrees of freedom of structures by limited

degrees of freedom, the structures are divided into many elements (Rachel et al., 2007).

These elements are connected by joint called node and make a grid named mesh.

Several modern finite element packages include specific components such as thermal,

fluid flow, electrostatic and structural working environments.

Generally, there are two types of analysis that is two-dimensional and three-

dimensional analysis. The structural of finite element analysis usually consist either

linear or nonlinear and it does generally characterize the elements. Usually finite

element models contain tens of thousands and possibly hundreds of thousands of

elements, resulting in hundreds of thousands of simultaneous equations

(Venkatasubramaniam et al., 2004). Usefulness of the finite element analysis result

depends highly on the pre-processing stage. Thus, defining an appropriate physical

model (mathematical model, geometrical simplifications, material properties, boundary

conditions and loads) and an adapted mesh in accordance with simulation goals is a

very difficult and time-consuming task. In practice, the modeling assumptions are still

mostly based on the user's experience (Bellenger et al., 2008). By using this tool, it

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